This invention relates to impulse ink jet devices and ink supply systems for such devices.
Impulse ink jet devices which provide a drop on demand in response to the state of energization of a transducer are typically supplied with ink from relatively small cartridges since the volume of ink consumed in an impulse ink jet device is relatively small as a normal rule. However, certain industrial applications of impulse ink jet devices require large volumes of ink over extended periods of time. For example, on-line printing of corrugated containers may require a plurality of ink jet print heads where each head comprises a large number of jets so as to produce relatively large characters and/or bar codes. Under these circumstances, a large volume of ink is used for extended periods of time. The use of small cartridges becomes impractical. For printing in this type of application, a relatively large ink supply is necessary, e.g., a container holding 125, 250, 500 or 1000 milliliter. The use of such a large ink supply does however pose certain problems for an impulse ink jet apparatus.
First, an impulse ink jet apparatus must be primed properly with ink in order to operate properly. Priming of an impulse ink jet requires that positive pressure be generated in connection with the supply of ink so as to force the ink through the ink jet chambers and the orifices of the ink jet while preventing the sucking of ink back through the orifices and the chambers upon completion of priming. One possibility for priming involves a bottle squeezing technique with some relief of the built-up pressure through the use of various types of valves including umbrella, duck bill and flapper valves. Such valves are required to be sensitive to back pressure while being strong enough to seal ink in during the squeezing phase. In addition, such valves may present problems of material compatibility with the inks used. Accordingly, it may be difficult to reliably design to meet the above-stated criteria. Another possibility includes a manually operated valve but this requires precisely timed manual procedures which may pose difficulties to operators in the field.
Priming of an impulse ink jet system may also be accomplished by pressurizing an air space above an ink reservoir. However, any increase in ink pressure in a container in which the ink reservoir is located will continue to force ink out through the ink jet device even after the pressure is removed. The device may therefore "weep" uncontrollably. Pressure could be applied directly to the container by puncturing a hole in the container in the air space above the ink which may also be used so as to relieve pressure within the container as soon as the pressure is removed from the container. This option, however, makes removal of partially filled containers messy as well as foreclosing on ecologically sound refilling policy.
Peristaltic pumps have been proposed for use in priming impulse ink jet apparatus wherein rollers are moved into contact with a tube containing ink, rolled along the tube containing ink and then separated from the tube so as to allow the free flow of ink through the tube. Such a mechanism is complex, expensive and may be difficult to implement in a variety of applications.